#first{
    width: 800px;
    height: 400px;
    border-width: 10px;
    border-color: green;
    border-style: solid;
    box-sizing: border-box;
    /* 内边距 */
    padding: 100px;
    /* 外边距 */
    margin-left: auto;
    margin-right: auto;
    margin-top: 100px;
    margin-bottom: 100px;
}
#second{
    width: 800px;
    height: 400px;
    border-width: 10px;
    border-color: green;
    border-style: solid;
    box-sizing: border-box;
    /* 内边距 */
    padding: 100px;
    /* 外边距 */
    margin-left: auto;
    margin-right: auto;
    margin-top: 100px;
    margin-bottom: 100px;
}